Ruthenium-arene (6-membered) complexes have been used as precursors of hydrogenation catalysts or hydrogen transfer catalysts. Recently, these ruthenium-arene complexes are also used as precursors of anti-tumor agents, thin film electrode materials for semiconductor devices or the like, and thus the demand for the complexes is ever increasing.
These ruthenium-arene complexes are generally produced by refluxing corresponding 1,3- or 1,4-cyclohexadienes and ruthenium (III) trichloride tetrahydrate in ethanol or methanol (see J. Chem. Soc., Dalton Trans (1974) p. 233).
Another method, under high temperature [RuCl2 (p-cymene)]2 was melted together with hexamethylbenzene, durene (1,2,4,5-tetramethylbenzene) or the like, which have higher boiling points than that of p-cymene, and allowing the compounds to react and exchange the arene moieties (see Inorg. Chem., 19 (1980) p. 1014-1021; and Inorg. Synth., 21 (1982) p. 74-78).